The present invention relates to a device for inserting a bipolar electrode structure through the vagina and cervix of a woman in labor and attaching it to the epidermis of a fetus. The electrode structure is designed to be operatively connected to an amplifier and a cardiotachometer for recording the fetal electrocardiogram and heart rate during labor and delivery.
For over seventy years monitoring of the fetal heart rate has been one of the important procedures in the management of labor. A number of electronic techniques have been developed for continuous recording of this data. Currently, the most successful techniques for fetal heart rate monitoring employ electrode attached directly to the scalp of the fetus.
U.S. Pat. No. Re. 28,990 issued to Dr. Edward H. Hon, is directed to an electrode structure which is believed to be the most widely used type employed today in the monitoring of fetal heart rate. The state of the art prior to the development of the device disclosed in that patent is amply illustrated in the references cited during the prosecution of the application for that patent.
The device of U.S. Pat. No. Re. 28,990 has a number of disadvantages. Firstly, the angularity of the outer guide tube must be kept relatively small, about 22 degrees, with respect to its primary longitudinal axis in order to permit the inner driver tube to rotate smoothly within the outer guide tube. The radius of curvature is about 12-13 inches. If the angle is too great the inner driver tube would cause friction at the bend and result in a jerky release of the inner drive tube preventing smooth continuous rotation of the electrode. All feel would be lost This small angle also mandates that the arms of the doctor be kept very low in relationship to the axis of the vagina of the patient, at the plane of the top of the bed the patient is lying on, in order to permit the device to be applied to the head of the fetus. This is especially true if the head of the fetus is high, as it often is in early labor. This situation may be present during the last few weeks of pregnancy or at the commencement of labor. In many multiparous and some nulliparous women, at the onset of labor the fetal head is above the pelvic inlet. In this circumstance, the head is referred to as high or "floating." Additionally, the cervical canal may be minimally (1-2 in) dilated an its axis makes an angle of 90-100 degrees with the axis of the vagina. This combination of factors viz., high head, minimal cervical dilation and axial misalignment makes electrode application extremely difficult with an electrode system when the guide tube curvature is too "flat" to negotiate the acute angles encountered in the foregoing circumstance.
A second disadvantage of this prior device is that the electrode is rotated by the physical rotation of the hand in order to implant the electrode in the head of the fetus. This is not a simple procedure and is inherently awkward as a complete turn of the driver tube is required and usually requires two separate turns of about 180 degrees each. In the interval between turns when the driver is released, it may "kick back" (due to friction at the curvatures), thus further complicating application. The turning action, coupled with the smooth guide tube, tends to create a rearward, away from the fetus, vector force during use. This may result in the electrode sometimes being withdrawn from the head of the fetus during rotation, preventing the implanting of the electrode in the head of the fetus.
Patents have disclosed guide tubes which can vary the angle of the guide tube, such as disclosed in U.S. Pat. No. 4,686,996 and U.S. Pat. No. 4,836,208 to Ulbrich. In the Ulbrich patent a flexible guide tube has a portion which is a flexible universal hinged member. The electrode holder is affixed to the end of the guide tube, and the entire guide tube is rotated. These patents evidence the inability of prior devices to increase the angle of the outer guide tube and still have an internal driver. With such devices, it would be difficult to apply the electrode due to the flexibility of the joint, and it could even move out of the line of the guide tube.
In the United States Patent to Murphy, U.S. Pat. No. 4,149,528 a highly flexible outside guide tube was used with flexible wires, without an inner drive tube. The increased angle of the outer guide tube required the elimination of the inner guide tube.
These patents resulted in devices that would be more difficult to use, more expensive than the currently acceptable and familiar device, and also less reliable.
The electrode of U.S. Pat. No. 4,321,931, issued to Edward D. Hon, avoids rotation of the hand. This patent provided a plunger rod arrangement for converting a linear pushing action into a rotary action at the electrode tip end for advancing and rotating the electrode at the same time. However, such a device may generate an even greater rearward vector force than the prior device since the physician reflexly pulls back on as any device that has a syringe-like action. Also, the angularity of the device was substantially the same as the original electrode of U.S. Pat. No. Re. 28,990.
Also, the outer guide tubes of the prior art electrode devices are smooth and are made slippery by the natural lubricating secretions present in the vagina. During application of the electrode there was no means of firmly holding the forward end of the guide tube to maintain gentle pressure against the fetus during application, or for determining the axial direction of the outer guide tube with respect to the axis of the head of the fetus.